Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2001-11-01
2004-08-03
Tran, Henry N. (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S082000, C315S169300
Reexamination Certificate
active
06771235
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and method for driving a light emitting panel using capacitive light emitting elements such as organic electroluminescence elements.
2. Description of the Related Background Art
In recent years, with the trend of increasing the size of display devices, thinner display devices have been required, and a variety of thin display devices have been brought into practical use. An electroluminescence display composed of a plurality of organic electroluminescence elements arranged in a matrix has drawn attention as one of the thin display devices.
The organic electroluminescence element (hereinafter simply called the “EL element”) may be electrically represented as an equivalent circuit as illustrated in FIG.
1
. As can be seen from
FIG. 1
, the element can be replaced with a circuit configuration composed of a capacitive component C and a component E of a diode characteristic coupled in parallel with the capacitive component C. Thus, the EL element can be regarded as a capacitive light-emitting element. As the EL element is applied with a direct current light-emission driving voltage across the electrodes, a charge is accumulated in the capacitive element C. Subsequently, when the applied voltage exceeds a barrier voltage or a light emission threshold voltage inherent to the element, a current begins flowing from one electrode (on the anode side of the diode component E) to the organic functional layer which is a light emitting layer so that light is emitted therefrom at an intensity proportional to this current.
The Voltage V-Current I-Luminance L characteristic of the element is similar to the characteristic of a diode, as illustrated in FIG.
2
. Specifically, the current I is extremely small at a light emission threshold voltage Vth or lower, and abruptly increases as the voltage increases to the light emission threshold voltage Vth or higher. The current is substantially proportional to the luminance L. Such an element, when applied with a driving voltage exceeding the light emission threshold voltage Vth, exhibits a light emission luminance in proportion to a current corresponding to the applied driving voltage. On the other hand, the light emission luminance remains equal to zero when the driving voltage applied to the element is at the light emission threshold voltage Vth or lower which does not cause the driving current to flow into the light emitting layer.
As a method of driving a display panel using a plurality of EL elements as described above, a simple matrix driving mode is known.
FIG. 3
illustrates an exemplary structure of a driver in accordance with the simple matrix driving mode. In a light emitting panel, n cathode lines (metal electrodes) B
1
-B
n
are arranged extending in parallel in the horizontal direction, and m anode lines (transparent electrodes) A
1
-A
m
are arranged extending in parallel in the vertical direction. At each of intersections of the cathode lines and the anode lines (a total of n×m locations), an EL element E
1,1
-E
m,n
is formed. The elements E
1,1
-E
m,n
which carry pixels are arranged in matrix, each have one end connected to an anode line (on the anode line side of the diode component E in the aforementioned equivalent circuit) and the other end connected to a cathode line (on the cathode line side of the diode component E in the aforementioned equivalent circuit) corresponding to the intersections of the anode lines A
1
-A
m
along the vertical direction and the cathode lines B
1
-B
n
along the horizontal direction. The cathode lines are connected to a cathode line scanning circuit
1
, while the anode lines are connected to an anode line drive circuit
2
.
The cathode line scanning circuit
1
has scanning switches
5
1
-
5
n
corresponding to the cathode lines B
1
-B
n
for individually determining potentials thereon. Each of the scanning switches
5
1
-
5
n
supplies a corresponding cathode line either with a bias potential Vcc (for example, 20 volts) or with a ground potential (zero volt).
The anode line drive circuit
2
has current sources
2
1
-
2
m
(for example, regulated current sources) corresponding to the anode lines A
1
-A
m
for individually supplying the EL elements with driving currents through respective anode lines, and drive switches
6
1
-
6
n
. Each of the drive switches
6
1
-
6
m
is adapted to supply an associated anode line with the output of the current source
2
1
-
2
m
or a ground potential. The current sources
2
1
-
2
m
supply the associated elements with such amounts of currents that are required to maintain the respective EL elements to emit light at desired instantaneous luminance (hereinafter this state is called the “steady light emitting state”). Also, when an EL element is in the steady light emitting state, the aforementioned capacitive component C of the EL element is charged with a charge, so that the voltage across both terminals of the EL element is at a positive value V
F
(hereinafter, this value is called the “forward voltage”) slightly higher than a light emitting threshold voltage Vth. It should be noted that when voltage sources are used as driving sources, their driving voltages are set to be equal to VF.
The cathode line scanning circuit
1
and the anode line drive circuit
2
are connected to a light emission control circuit
4
.
The light emission control circuit
4
controls the cathode line scanning circuit
1
and the anode line drive circuit
2
in accordance to the image data supplied from an image data generating system, not shown, so as to display an image represented by the image data. The light emission control circuit
4
generates a scanning line selection control signal for controlling the cathode line scanning circuit
1
to switch the scanning switch
5
1
-
5
n
such that any of the cathode lines corresponding to a horizontal scanning period of the image data is selected and set at the ground potential, and the remaining cathode lines are applied with the bias potential Vcc. The bias potential Vcc is applied by regulated voltage sources connected to cathode lines in order to prevent crosstalk light emission from occurring in EL elements connected to intersections of a driven anode line and cathode lines which are not selected for scanning. The bias potential Vcc is typically set equal to the light emission regulating voltage V
F
(Vcc=V
F
). As the scanning switches
5
1
-
5
n
are sequentially switched to the ground potential in each horizontal scanning period, a cathode line set at the ground potential functions as a scanning line which enables the EL elements connected thereto to emit light.
The anode line drive circuit
2
conducts a light emission control for the scanning lines as mentioned above. The light emission control circuit
4
generates a drive control signal (driving pulse) in accordance with pixel information indicated by image data to instruct which of EL elements connected to associated scanning lines are driven to emit light at which timing and for approximately how long, and supplies the drive control signal to the anode line drive circuit
2
. The anode line drive circuit
2
, responsive to this drive control signal, individually controls the switching of the drive switches
6
1
-
6
m
to supply driving currents to associated EL elements through the anode lines A
1
-A
m
in accordance with the pixel information. In this way, the EL elements supplied with the driving currents are forced to emit light in accordance with the pixel information.
Next, the light emitting operation will be explaining with reference to an example illustrated in
FIGS. 3 and 4
. This light emitting operation is taken as an example in which a cathode line B
1
is scanned to have EL elements E
1,1
and E
2,1
emit light, and subsequently, a cathode line B
2
is scanned to have EL elements E
2,2
and E
3,2
emit light. Also, for facilitating the understanding of the explanation, in
FIGS. 3 and 4
, an EL element which is emitting light is represented by a
Ishizuka Shinichi
Ochi Hideo
Sakamoto Tsuyoshi
Pioneer Corporation
Sughrue & Mion, PLLC
Tran Henry N.
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